Study On Phosphogypsum-Based Modified Calcium Sulfate Whiskers With Large Aspect Ratio By Glycerol-Hydrothermal Method

Phosphogypsum (PG) is a kind of industrial residue with various chemical components, complex structure, and calcium sulfate dihydrate was the main content. PG is harmful to environment, but it’s also good resource. So utilizing PG comprehensively was significant. At present, PG was used mainly for production of gypsum brick and cement retarder, preparation of calcium sulfate whisker (CSW), and as soil improving agent etc.. Owing to the high strength, low toxicity and low production cost, preparation of PG-based modified CSW with large aspect ratio has received researchers’extensive attention. The morphology, aspect ratio and synthetic ratio of CSW were affected by preparation method, preparation system, preparation condition, the kinds and amounts of additives and other factors. Therefore, it is very essential to explore suitable method, system, additive, modified agent and process parameters on the production of PG-based modified CSW with large aspect ratio.In this paper, PG-based CSW was prepared by autoclaved glycerol-hydrothermal method and atmospheric glycerol-hydrothermal method. The preparation process parameters were optimized. The preparation mechanism of CSW and reaction mechanism of glycerol were also investigated. Moreover, the technological conditions of modification and mechanism of CSW modified by wet-process were explored. Besies, the preparation and modification of CSW with integrated process was investigated. And the mass production of large aspect rato modified CSW was successful. The main research contents are as follows:The orthogonal experiment results showed that the optimization of process parameters was that the initial solid-liquid ratio was1:20, reaction temperature was140℃, reaction time was2h, V (glycerol)/V (water) was50%, ball milling time was1.5h, dry temperature was100℃in the process of preparation of CSW by autoclaved glycerol-hydrothermal method. The morphology of CSW was uniform, with average aspect ratio of55shown in SEM image, and synthesis ratio of about95%. The XRD pattern was shown that the phase of CSW was calcium sulfate hemihydrate. The content of soluble phosphorus was0.19%measured by standard curve method. And its removal rate was49%.In the process of preparation of CSW by atmospheric glycerol-hydrothermal method, the results showed that the optimization of process parameters was that the initial solid-liquid ratio was1:20, reaction temperature was110℃, reaction time was2h, V (glycerol)/V (water) was more than0.6, ball milling time was1.5h, dry temperature was100℃. The morphology of CSW was uniform, with average aspect ratio of120shown in SEM image, and synthesis ratio was98%. The XRD pattern was shown that the phase of CSW was calcium sulfate hemihydrate. The content of soluble phosphorus was0.19%measured by standard curve method. And its removal rate was49%.In the process of modification of CSW by wet-process with stearic acid, the results showed that the optimization of process parameters were that stearic acid of4%, modification temperature of90℃, modification time of20min, stirring speed of1250r·min-1. Its activation index is up to0.99. It was shown that C=O stretching vibration absorption was at about1750cm-1. The stretching vibration of CH3and CH2were at2917cm-1and2849cm-1. And1375cm-1was the bending vibration of C-H. Besies, hydrogen bonds existed at3500to3300cm-1. CSW was modified by stearic acid with chemical and physical adsorption.Preparation and modification of CSW by integration process was that stearic acid of4%was added and stirred for30min in this system, when the preparation of CSW by atmospheric glycerol-hydrothermal method was over and the temperature of system was down to90℃. The morphology of CSW was uniform, with average aspect ratio of110shown in SEM image, and synthesis ratio of98%. The XRD pattern was shown that the phase of CSW was calcium sulfate hemihydrate. The content of soluble phosphorus was0.19%measured by standard curve method. And its removal rate was49%. Othermore, its activation index is up to0.99.500L industrial production of modified CSW was achieved by preparation and modification with integration process. The morphology of CSW was uniform, with average aspect ratio of90shown in SEM image, and synthesis ratio of98%. The XRD pattern was shown that the phase of CSW was calcium sulfate hemihydrate. The content of soluble phosphorus was0.21%measured by standard curve method. And its removal rate was48%. Moreover, its activation index was up to0.99.